Mechanical switches may be used to, for instance, indicate whether an environmental condition such as pressure, temperature or linear displacement is above or below a predetermined threshold. Further, the mechanical switch may be coupled to, for instance, a visual indicator associated with an environmental condition or a mechanical relay or a logical input associated with a control device.
Mechanical switches have been used in electromechanical devices for many years. Unfortunately, they have many shortcomings. For instance, mechanical switches are limited by their mechanical construction. Among other things, mechanical switches are known to provide poor reliability, poor stability, limited operational lifespan, relatively low accuracy, contact degradation, undefined hysteresis, and limited sensitivity to vibration shock, particularly when compared with electronic switches.
Unlike the mechanical construction of mechanical switches, electronic switches use solid-state technology and do not have the same restrictions or limitations that mechanical switches have. In many instances, electronic switches improve the limitations of mechanical switches, e.g., improving operational life, by several orders of magnitude. Advantageously, electronic switches may implement functions that cannot be implemented in mechanical switches, e.g., latched output(s), multiple thresholds, timed delays, and the like.
Today, there are numerous devices that utilize mechanical switches. Unfortunately, while it may be desirable to implement an electronic switch in the place of these mechanical switches, difficulties often forbid such replacement. For example, electronic switches may require a permanent power supply for the electronics and the sensor in the switch. In some instances, designers have supplied power via an additional wire to the electronic switch. Adding a power supply wire often requires rewiring the entire system in which the switches are part. Such rewiring is often expensive and difficult.
FIG. 1 illustrates a prior art system 100 having a three-lead electronic switch system adapted to replace a mechanical switch. In FIG. 1, the switches are implemented using metal oxide semiconductor field effect transistors (MOSFET) and are controlled by the electronic circuit, which may evaluate the output of the sensor by comparing it to a predetermined value. While the sensor is displayed as a Wheatstone bridge in FIG. 1, other types of sensors may be used. The configuration of FIG. 1 has a disadvantage of requiring an additional connection to provide a supply voltage to the electronic circuit and the sensor. Such configuration may require additional wiring or wiring changes, which may be expensive and labor intensive. Further, such configuration may require significant logistics such as documentation of the wiring or connector changes, which may render the replacement of the mechanical switch unfeasible despite the advantages of such a replacement.